1. Field of the Invention
The present invention generally relates to an image sensing array of an optical touch system, in particular, to a method for defining effective pixels in an image sensing array of an optical touch system.
2. Description of Related Art
Along with rapid development of technology, a touch-sensing electronic product has become a main trend of the market. Among resistive, capacitive, and back projection touch screens being used in the past, the capacitive touch screen provides the most satisfactory performance, and yet it requires the most expensive cost. Moreover, the cost of the capacitive touch screen increases with its screen size, and its application is thus limited. An optical touch screen that utilizes an optical lens to detect a touched position has been proposed as an alternative to the capacitive touch screen. The optical touch technology has various advantages such as low cost and high accuracy, which is more competitive in the market. It thus has also become an option for a large-sized touch screen.
In general, the optical touch screen performs sensing by using a plurality of optical sensing modules including light sources and image sensing arrays at edges of the screen after the light provided by the light sources are reflected back to the image sensing arrays from a light-reflecting object. The optical touch screen could be categorized into an interruptive architecture and a reflective architecture.
In an interruptive optical touch technology, reflective strips or light-emitting strips are configured at the periphery of the touch area. When a touch object is located on the display surface and interrupts a part of the reflected or emitted light, an optical sensor would sense shaded areas caused thereby, and the location of the touch object may be calculated accordingly. In a reflective optical touch technology, reflective substance on the touch object or to project light is added on a touch object. When the touch object is located on the display surface, an optical sensor would sense the light reflected from the touch object, and the location of the touch object may be calculated accordingly.
Therefore, in the optical touch technology, in order to comply with the fundamental principles of the optical touch technology, it is important to make sure that the light reflected back from a light-reflecting object is able to be received by the optical sensor. However, it would be difficult to maintain an even surface for a large-sized touch screen, and the light may be reflected to other areas which are not able to be received by the optical sensor. A conventional line sensor may be replaced by an area sensor with a larger light receiving range to solve such a problem. However, all signals received by an image sensing array of the area sensor would form a two-dimensional signal array. During touch detection, the signal received by each of the image sensing pixels in the image sensing array is required to be analyzed so as to obtain a pixel with maximum intensity in each horizontal pixel and thereby obtain the high reflection signals for touch detection. Thus, as compared with the line sensor, the area sensor may take much more time on signal detection.
The existing technique has been extended to define a pixel among each horizontal pixel of the image sensing array of the area sensor that is able to obtain a highest reflection signal for touch detection at a factory production stage. Take a 1600×512 image sensing array as an example. The existing technique takes 1600×512 times of computation to determine the sensing pixel in each horizontal pixel which is able to receive a signal with high intensity. The production may be affected due to a large amount of computation.